This invention provides a process for the preparation of polyamide polymers. The process described herein has environmental advantages over known processes for preparing these products due to the reduction of emission gases in the process. The product produced by the process of the present invention also has a lower temperature history and thus improved quality, as judged by bishexamethylene triamine content, compared to products prepared by previously known processes.
Japanese Patent Application No. 4-93323, published Mar. 26, 1992, discloses a process for the preparation of polyhexamethylene adipamide comprising the steps of
(a) Step 1 comprising polymerizing in the solid phase of an equimolar salt of adipic salt (sic., "salt" should be "acid") and hexamethylene diamine while replenishing the hexamethylene diamine in an amount commensurate with the amount of hexamethylene diamine which has escaped, so as to prepare a prepolymer; PA1 (b) Step 2 comprising heating and melting the prepolymer from Step 1 and cooling for resolidification; and PA1 (c) Step 3 comprising polymerizing in the solid phase the solidified product from Step 2. The application further discloses that failure to implement each of the above three steps in the prescribed order will not permit generating a polyhexamethylene adipamide of this invention. PA1 a) polymerizing under conditions such that the reacting mass never completely liquefies (i.e., at reaction temperatures below the melting transition temperatures of the initial materials, the intermediate condensation products and the end products), an oxygen free equimolar salt of a dicarboxylic acid and a diamine PA1 b) further polymerizing the prepolyamide product of step 1 in the solid phase to a polyamide of desired molecular weight and then cooling the product in an oxygen-free environment. Nitrogen flow control during cooling can be used to ensure that the final product has the desired moisture content. PA1 a) polymerizing under conditions such that the reacting mass never completely liquefies (i.e., at reaction temperatures below the melting transition temperatures of the initial materials, the intermediate condensation products and the end products), an oxygen free aminocarboxylic acid PA1 b) further polymerizing the prepolyamide product of step 1 in the solid phase to a polyamide of desired molecular weight and then cooling the product in an oxygen-free environment. Nitrogen flow control during cooling can be used to ensure that the final product has the desired moisture content. PA1 a) polymerizing under conditions such that the reacting mass never completely liquefies (i.e., at reaction temperatures below the melting transition temperatures of the initial materials, the intermediate condensation products and the end products), an oxygen free equimolar diammonium dicarboxylate salts composed of one or more diamines and one or more dicarboxylic acids PA1 b) further polymerizing the prepolyamide product of step 1 in the solid phase to a polyamide of desired molecular weight and then cooling the product in an oxygen-free environment. Nitrogen flow control during cooling can be used to ensure that the final product has the desired moisture content.
U.S. Pat. No. 5,128,442 discloses a process for the preparation of linear polyamide in which a solid salt of a diamine and a dicarboxylic acid having a content of catalytically effective phosphorous compound is heated in the solid phase to below the melting point of said salt, using an inert gas to continuously remove the water formed during the condensation reaction to give a precondensate. There is no disclosure of operation in the absence of the phosphorous containing catalyst nor in the absence of the nitrogen purge, nor in the presence of additional amine.
U.S. Pat. No. 4,925,914 discloses a process for the preparation of high molecular weight homopolyamides from a nylon salt, uniformly preblended with a solid hypophosphite catalyst, dispersed in a liquid, aliphatic hydrocarbon. There is no disclosure of operation in the absence of the solid hypophosphite catalyst nor in the absence of the liquid, aliphatic hydrocarbon.